Doctor blades extending over a considerable length, and cooperating with ink rollers of substantial length, require adjustment along their length to provide for selective engagement of the doctor blade across the inking cylinder. One such adjustment arrangement is shown, for example, in German Utility Model DE-GM No. 77 30 668. In this arrangement, a plurality of ink doctor blade adjustment pins are provided, each supplied with an outer thread which is screwed into a tapped bore formed on a fixed doctor blade support frame. Upon rotation of the respective adjustment pins, the axial position of the pins will be changed and an adjusting movement is transferred to the doctor blade itself. To permit replacement of the doctor blade, an indication of the adjustment position of each pin is provided, for example by providing at the end of the pin an indicator scale which cooperates with a reference marker.
The subject matter to be printed may require that the doctor blade adjustment pins so adjust the doctor blade that in some locations it is very close to the inking rollers whereas, at immediately adjacent adjustment positions, the maximum possible nip or gap between the doctor blade and the ink cylinder is provided. In such arrangements, the flexibility of the doctor blade may be insufficient to completely follow the controlled adjustment, since it cannot be bent in accordance with the adjustment positions which are commanded. Play will thus arise between the doctor blade adjustment pins adjacent the pin or pins which are extended to their maximum position--that is, where the smallest gap is to occur--so that the pins adjacent this smallest gap will not transfer adjustment forces on the doctor blade itself. The position of the pins then does not correspond to the actual position of the doctor blade in these ranges, the doctor blade forming what might be termed a bridge across the pins immediately adjacent the adjustment pin commanding the smallest gap or nip. Scales attached to these pins adjacent the smallest-gap pin thus will indicate an incorrect adjustment position.
It has been proposed to provide electrically controlled positioning apparatus and indicators which are to control the position and indicate the position of the respective doctor blade adjustment pins--see German Disclosure Document DE-OS No. 21 64 351. The indications derived from electrical indicators coupled to pins adjacent a pin commanding a minimum gap or nip likewise will be erroneous.